Materials and hydrodynamic aspects of the interaction of foreign materials with blood are reviewed. A possible method for preventing platelet and protein adhesion to foreign surfaces, which makes use of perfusion of physiologic fluid through porous materials is suggested. Results of preliminary experiments with such a method are described. Further studies are proposed where the range of porosity and material variables will be examined, within which platelet and protein adhesion can be prevented at reasonable perfusion rates. Hydrodynamic experiments will be performed with latex suspensions and human whole blood to determine the steady state velocity distribution in tube flow with steady wall perfusion. Particle diffusion measurements will be made simultaneously and the results compared with the particle distribution expected from diffusion-convection theory. Similar measurements will be made using pulsed perfusion. Results will be used to establish approximate hydrodynamic criteria for the prevention of formed element adhesion in perfused systems.